1. Field of the Invention
The present invention relates to a mechanical pressing machine so designed that a slider is reciprocally moved utilizing a cam mechanism.
2. Description of the Related Art
Mechanical pressing machines for producing by press working small-sized electronic components or the like at a high speed and with a high accuracy have been conventionally known. One type of such pressing machines includes a horizontal input shaft rotatably mounted in a housing, a cam mounted concentrically on the input shaft, and a slider mounted in the housing for vertical sliding movement and surrounding the cam. The slider has a die fixed to its lower end and carries a cam follower which is always in engagement with the cam, so that when the cam is rotated together with the input shaft the slider effects vertical sliding movement. The pressing machine of such type is disclosed in JP-Y2-5-22394 and JP-Y2-22395, for example.
In mechanical pressing machines utilizing a cam mechanism, it has been conventionally known to incorporate therein a dynamic balancer. The dynamic balancer includes a balance weight which is moved vertically in a direction opposite from the vertical movement of a slider, thereby offsetting or canceling an unbalanced inertial force generated during the vertical movement of the slider to suppress vibration during operation of the pressing machine. The incorporation of the dynamic balancer thus realizes to conduct a press working at a high speed and with a high accuracy. One type of such pressing machine incorporating a dynamic balancer includes a slider and a balance weight connected to each other through a link mechanism. The pressing machine also includes a plate cam mounted on an input shaft for controlling movement of the slider and a plate cam mounted on the input shaft for controlling movement of the balance weight, so that the slider and the balance weight are controlled by the plate cams to reciprocally move in directions opposite from each other. Such pressing machine is disclosed in JP-A-9-66395, for example.
In each of the prior art machines disclosed in JP-Y2-5-22394 and JP-Y2-5-22395, the slider is mounted in the housing for vertical sliding movement and surrounds the cam, and the cam and the slider constitute a yoke cam mechanism. Such an arrangement suffers from a problem that the slider is increased in size, resulting in an inertial force increased during the operation. This is one cause obstructing an increase in operation speed of the pressing machine. Another problem resides in that it is difficult to incorporate in the pressing machine the dynamic balancer in such a manner as to make it function satisfactorily. Namely, when the yoke cam mechanism is employed, the single cam is interposed between the two cam followers provided on the slider and for this reason, it is difficult to arrange the dynamic balancer at a location symmetric with the slider with respect to the cam.
In the prior art machine disclosed in JP-A-9-66395, the plate cams for controlling sliding movement of the slider and the plate cam for controlling sliding movement of the balance weight are provided separately from each other, and the link mechanism is used. This suffers from a problem that many elements are required to drive the slider and the dynamic balancer, resulting in an increase in size of the pressing machine. There is also a problem that the degree of freedom for designing the cam shape is limited, since the cams and the cam followers have to be preferably contacted with each other even under the presence of the link mechanism.